The present invention relates to a wireless LAN (local area network) base station, and, more particularly, to a wireless LAN base station capable of carrying out automatic matching for radio channels.
As known, an LAN is a local network system for connecting a variety of computers such as a server, workstation, personal computer, or the like, dispersedly provided in a comparatively narrow area such as within the same building, within the same site, or the like, In the LAN, it is popularized in an application form in which one transmission medium is commonly used by a multiplicity of hosts. An MAC (media access control) is well known as transmission control technology essential for the LAN. The MAC is an access control for a plurality of nodes to smoothly and commonly use a local cable. The MAC is positioned at a lower sublayer of a data-link layer of OSI (open systems interconnection) model. The MAC cooperatively works with LLC (logical link control) of an upper sublayer of the data-link layer to realize a function of the data-link layer.
An MAC address is a standardized data link-layer address required for every port or device connected to the LAN. Another device in the network identifies the position of a specific port in the network by use of the address for creating and updating a routing table and data structure. The MAC address has 6 byte long and is defined by the IEEE (Institute of Electrical and Electronics Engineers). The MAC address is also known as a hardware address, MAC layer address, or physical address.
Moreover, the wireless LAN is an LAN using a transmission path such as an electromagnetic wave (radio wave), light (infrared ray), or the like, other than an electric wire (wire cable).
Normally, mobile radio communication employs a cell system. The cell system is a system in which a service area is divided into several areas (cells), each of the divided cells has a base station, and a plurality of the base stations cover whole service area. The cell system, in order to effectively use radio frequencies, uses radio channels of the same frequency between the cells maintaining a space which prevents from mutual interference or jamming. Accordingly, the cell system has a characteristic that the service area can be expanded even with limited frequency bands.
A telephone system by use of the wireless LAN comprises a main device, a plurality of wireless LAN base stations connected to the main device through a cable LAN, and a plurality of radio telephones for performing communication with the wireless LAN base stations through the wireless LAN. Each wireless LAN base station has an SSID (service set ID) as a zone identifier. The SSID is an arbitrary character string composed of 32 or less characters.
As a committee aiming at standardization of the wireless LAN, the IEEE 802.11 Committee is known. The IEEE 802.11 Committee stipulated the IEEE 802.11b as specifications for the standardized wireless LAN in September, 1999. According to the IEEE 802.11b, frequencies of 2.4 GHz band are used, and a spectrum diffusion communication direct diffusion system (SS-DS) is used for a modulation system. The SS-DS is the most popular system at the moment. Transmission rates thereof are 11 Mb/s and 5.5 Mb/s.
On the other hand, in Japan, the Wireless LAN Committee of the Telecommunications Technology Council submitted a report on the frequency bands and the like of the wireless LAN in July, 1992, and the Ministry of Posts and Telecommunications approved allocation of the radio wave. In other words. in Japan, for the wireless LAN of the frequencies of 2.4 GHz band stipulated by the IEEE 802.11b, radio channels of No. 1 to No. 14 CH (channel) can be provided using the frequencies from 2412 MHz to 2484 MHz in unit of 5 MHz.
However, as described above, in the IEEE 802.11b, radio signals are to be transmitted by use of the direct spectrum diffusion system as the modulation system, thus a frequency band of 20 MHz is required for one channel. Therefore, in order to make a channel not to be interfered by another channel, a frequency band enough for 4 channels is required.
Accordingly, each LAN base station requires setting of the radio channels by contriving such that interference with other channels may be avoided. However, when the radio network expands, the number of the wireless LAN base stations also increases, and therefore setting of the radio channels in each wireless LAN base station, while avoiding the interference, becomes difficult.
As a technical paper in association with the present invention, the official gazette of PCT Japanese Translation Patent Publication No. 7-508385 (hereinafter referred to as a technical document 1) is known. The technical document 1 discloses a radio frequency communication system having a plurality of transceivers operated by a variety of frequencies within a predetermined range. In particular, the technique disclosed in the technical document 1 provides a method for and a device of selecting an operating frequency, to be used in communication equipment which commences operation in the radio frequency communication system, from within the above-described predetermined range. For example, speaking of the method disclosed in the technical document 1, the communication equipment carries out the following operation. Namely, the communication equipment carries out a step of scanning a set of frequencies within the above-described predetermined range at an operating position thereof, a step of storing into a memory a table of information corresponding to a signal detected during the scanning, a step of checking out the number of interfering paths in association with respective scanning frequencies, and a step of selecting a frequency having the least number of the associated interfering paths from within the above-described predetermined range.
However, the technical document 1 only discloses the technique by which respective communication equipment can select a frequency having the least number of the interfering paths, and does not pay any consideration to the number of the near-by base stations. Necessity of the information regarding the number of the near-by base stations will become clearer with progress of the description.